I am busy with the geometric design of an existing road, with the aim being same alignment but wider lanes, so first step is to create a centreline that follows the existing one.
the first snag that i have come across is that the existing CL seems to have spiral transitions on some of the curves. Now the transition/spiral length is based on the superelevation run-off which is based on the curve radius. bit of a catch 22 so how do i work it backwards since the length of the transition affects the curve radius.
What i have done for now is to create a best-fit curve without a spiral and then work out the super run-off length from that. use that length for the spiral length and then adjust the curve the difference in curve diameter is not changed hugely.
Second question is this is a mountainous road with some tight curves (50m radius) the new road has 3.5m lanes. with this lane width should i be looking at widening the lanes on the curves (not sure if the sheer drop-offs will cater for any additional width anyway, but interested to know)?
the first snag that i have come across is that the existing CL seems to have spiral transitions on some of the curves. Now the transition/spiral length is based on the superelevation run-off which is based on the curve radius. bit of a catch 22 so how do i work it backwards since the length of the transition affects the curve radius.
What i have done for now is to create a best-fit curve without a spiral and then work out the super run-off length from that. use that length for the spiral length and then adjust the curve the difference in curve diameter is not changed hugely.
Second question is this is a mountainous road with some tight curves (50m radius) the new road has 3.5m lanes. with this lane width should i be looking at widening the lanes on the curves (not sure if the sheer drop-offs will cater for any additional width anyway, but interested to know)?